Method of making a transducer diaphragm



U dStat wnee METHOD or MAKING A 'mANsn cnR an I Luth,?9% 1 st S Holland,Midi.

Filed pi s, 1958, S01. No. 758,597 7 invention relates to a transducerdiaphragm and a sothat the diaphragms have poor transient response." In

order to have good transientresponse, the di method ofmakingthe same inwhich the diaphragm has started abruptly byqenergization of thevoicecoil and must above desired characteristics.

a One of the features ofthis invention is to provideatransduccrdiaphragm comprising a lightweight uncompressed fibrous sheetand a self-sustaining cured resin coating on the sheet, the sheet beingexpanded and subfimfially ssm s er b e. c i eet and resin 'has anapparent density less thane itsfabsolute ther feature of the inventionis toprovide an i1nproved method ofmaking a transducerv diaphragm. com

prising'providing a mold having a surface of the desired diaphragm shapeand contour, applying to the a thin fibrous sheet material, applying aliquid thermosetting resin and curing the resin while the material andresinare relatively free andunconfined;

The transducer diaphgrams of this inventionhave the rac mes 0st. 19.,tes

with most fibrous materials will alsocanse an andlooseningof'the fib'ersand a setting of they The dried sheet material .with the is then with aliquid thermcsetting and is partially cured to adherent yet flexible Thesheet material isthen removed from the mold, trimmed at the edges andcenter to the'shape [and dimensions of the diaphragm, r'eplacedon themold surface and theatre is completed to produce a strong,self-sustaining low'density p fl -f f a v The following examples areillustrative only of methods and diaphraginseirilzyodyiug'"theinvention: 7

t Exar;nple1 l'fln this'exainple, I diaphragmwas provided fora, 10 inchcone. A disc 01 cotton muslinhaving athreadcount of about) it 40 andsuch as a loudspeaker cone must be capable of being about} inilsY thickwa @t' incircular shapewith a diameter about'two' inches'la'r'gerthan'the diameter of the cone. A 5 solution; of polyacrylamide was prepared,with the polyacrylamide being of such grade to produce a viscosity ofabout 5 in the*5 water solution.

The mold was he'atedin an oven to about 115" c. and a mold release waxapplied to the mold with the wax being made up of equal parts ofparalfin wax and carnauba wax to-which enough Stoddard Solventhad beento produce a soft paste. After the mold had been coated" with thisrelease wax, the cotton muslin was dipped in water, most of thewatersqueezed out until the muslin Other; features and advantages of the"invention be apparent from the following description of. certain em--bodimentsthereof. In producing the diaphragms ofv this invention, amoldof the desired shape and contour is used., The uncured diaphragmiisarranged on thesurface of this mold and cured in afrelatively andunconfined state under substantially no pressure so that the resuln'ngwill have a, low apparent gravitywhen compmd to its absolute gravity. Asis well known, a material in.

an ,expanded'open statewill have a specific gravity, called the,apparentspecific gravity,.that ismuch less than its absolute or trueor. density. Thus, for example, pure cellulose has an absolute ortrueldensity of.l.583. Yet, certain forms of cellulose'such ascertain,ty es, of wood may have a density as lowas 0.32.

In'fthis invention, any type of mold may be usedas desired. 7 This moldmust have a suriace, preferably a1 convex surface when a cone is beingmolded, has,

generally the shape and contours of the diaphragm. In thegeneralprocess, a sheet of. fibrous material somewhatlarger than-thefinishedjdiaphragm is placed on the mold surface and is coated withvabinder:

with the solution,-it is heated waive-on the water time, the mold and mewere from was just damp and the muslin then stretched smoothly overthemold surface. lmmediatelythe above polyacryl' amide solutionswasbrushed on the cloth, with suflicient pressure being applied to pressthe cloth down in contact with.the vmold and to coat the cloththoroughly. The heated mold "caused. theJvater to. steam; thereby.

oi the .waterand-causingthecotton fihcrsftoiswell.

mold wasthen placedinthe oven to.,drivefofl 1M1 traces of the water. :1,I H i when the mold andrnuslinfwas dry, the mold; was

rcmovedgtrom the ovenand.a liquid resin mixture of 1'2- grams ofiepoxyresin (epoxideeguivalent 17S2l'0)"fand 3 grams of tri ethylenetetrarninc wasi'bruslied 'q fthe muslin in the mold; 'The mold and thethusly coated muslin were then returned tojthejoven and permitted toremain there until the resin had, reached an stagejinji s cuiin'gibutbefore theresin-had hardened I to the oven for completion of the curewhich took about four, or five minut M the ind pfvtvhq quip and theconeremoved from the mold.

g this rocedure, the muslin sheet and appliedcoating materials'were f ylw' si m l ns 99 was. extremely strong, yetfihad sound In example,substantially the same procedure was f l ws s tha *P YF: fis t e. 9 m slt sa a 1 5 sm a l sf a s -mg -i' c n o sewar s w mid "a maxim miidepthfstjthlefcenter of 2% inches, an outside diameierbrswi' aconventional mold i loudspeaker I tailmfi finished cone' had a centervoice coil opening of .1 inch diameter. The resin used had the followingingredients:

Epoxy resin--epoxide equivalent 175-210- 140.

Epoxy resinepoxide equivalent 225490- 60 parts/wt. Titanium dioxide 3.Precipitate calcium carbonate 3-4 microns 27. f--the above a 12.Triethylene tetramine 3.

In this example, the cloth was wet as set outabove and uniformly formedin the hot mold with polyacrylamide as described above in Example 1.:The mold and shaped cloth was held in the oven at 135 C. for /2 minutes,and removed from the oven and the resin applied to the c'oth, returnedto the oven and the resin precured for five minutes. At the end of thistime, the partially cured cone is removed from the mold, punched andtrimmed as described above and again cured for three minutes in the ovenas set out above before the finished cone was removedfrom the oven. Theentire procedure took about 17 minutes. The resulting cone weighed 13%grams, had anaverage thickness of mils .and a specific gravity of 1.15to 1.18.

This compares with conventional materials cured under heat and pressurewhich have specific gravities of from 1.45 to 1.5. The new cone hadexcellent strength and when installed in a loudspeaker was found to haveexcellent transient responses. The frequency response on sweep frequencywas free of peaks and valleys.

Y Example '3 V In this example, the cone was prepared by the method setout in Example 2, but here a polyester resin was used instead of theepoxy resin. The polyester resin was a copolymer of an alkyd resin andstyrene. The polyester resin was a liquid with a styrene content ofabout 35% by weight. The resin mixture used had a viscosity of about 1poise and the following constituents:

a .Grams Polyester resi Qailcillm carbonate 3 Titanium dioxide l 0.3Peroxide catalyst 0.3

p The same procedure in making the diaphragm was followed here as wasfollowed in Example 2. The initial curing time. was 8 minutes in theoven at 115 C. and the final curing was for 81 minutes. The cone weighed14% grarnsand had a mean thickness of 14 to 15 mils.

Example 4 In this examplea series of cones were made by the method ofExample 2, using the following b nder solutions:

Methylcellulose 5% sol. in water of 15 cps.

methylcellulos'e.

Methylcellulose 30% sol. in water of 15 ,cps.

' methylcellulose.

Hydroxyethylcellulose- 5%-.-300 .cps. I-LE. cellulose. Sodium carboxymethyl- In this example a series of cones were prepared. bythe method ofExample 2, using in place of the triethylone tetramine, ethylenediamine, diethylene-triamine,and tetraethylene pentamine.

Example 6 In this example, the cone was prepared by the method set outin Example 2, using the same materials and curing temperatures. The moldwas such that the resulting cone had a maximum depth at the apex of 2 /8inches: and a diameter of 10% inches. The cone had a central opening fora 1 /2 inch voice coil and weighed 19 grams and had a thickness of 13-15mils. When the cone was fitted as a partof a loudspeaker, the frequency.response was found to be very smooth, extending down to approximatelycycles per second' and had a barely. audible harmonic response. The highfrequency response extended to 15,000 cycles and transient response wasvery good.

In. general, the diaphragm of this invention is made of fibrous sheetmaterial preferably produced n'om fabrics such as cotton, wool, glasscloth or the various synthetic fabrics suchas nylon, Orion and Dacronand various combinations of these. The resins that may be used are anythermosetting resin that can be applied in a liquid state and that canbe cured to a strong solid. These include epoxy resins, phenol or ureaaldehyde resins and the various copolymer resins of alkyds and monomerscopolymerizable therewith particularly styrene.

The water soluble binder or stiflener which is preferably initiallyapplied to the fibrous material sheet includes polyacrylamide', thevarious alkyl celluloses, hydroxyalkylcelluloses, and alkali metal saltsof carboxy akyl celluloses and polyacrylamide.

Having described my invention as related to the embodiments set outherein, it is my intention that the invention be not limited by any ofthe details of descrip-' tion, unless otherwise specified, but rather beconstrued broadly within its spirit and scope as set out in theaccompanying claims.

I claim:

1.1Tl'1e method of making a transducer diaphragm,

' comprising: providing a mold having a surface of the desired diaphragmshape and contour; applying to said surface a thin fibrous sheetmaterial; wetting said sheet material with water to aid in obtainingintimate contact of said material with the mold; heating said sheetmaterial to above the boiling point of water to drive ofi the water andloosen thefibers in the material; applying to said material a liquidthermosetting resin; andcuring said resin while said material and resinare free and unconfined.

2. The method of making a transducer diaphragm, comprising: providing amold having a surface of the desiredldiaphragm shape and contour;applying to said surface a'thin fibrous sheet material; wetting saidsheet material with water to aid in obtaining intimate contact of saidmaterial wth the mold; coating said material with a water solution of abinder; heating said sheet material to above the boiling point of waterto drive oif the water and loosen the fibers in the material; applyingto said material a liquid thermosetting resin; partially curing theresin-to as'elf-sustaining condition to form a blank; removing the'blank from the mold and cutting it to the desired dimensions; replacingthe blank in the mold; and curing said resin while said material andresin are free and unconfined. V

3. The methodof claim 2 wherein said binder is a solution of a-member ofthe class consisting of polyacrylamide, the alkyl c'elluloses, the.hydroxy alkylcelluloses,

5 alkali metal salts of carboxy alkyl cellulose, and alkali metal saltsof polyacrylamide, and said resin is a member of the class conssting ofepoxy resins, phenol aldehyde resins, urea aldehyde resins, andalkyd-styrene copolymers. 5

References Cited in the file of this patent UNITED STATES PATENTS1,759,387 Bateholts May 20, 1930 10 Charters Apr. 19, 1938 NagelvoortFeb. 14, 1939 Fletcher Aug. 4, 1942 Gerathy Aug. 27, 1946 Nebesar Nov.11, 1952 Brennan June 2, 1953 Nottebohm Oct. 4, 1955 Pessel Feb. 7, 1956Lampman Mar. 27, 1956

